Structure and diversity of mycorrhizal fungi communities of different part of Bulbophyllum tianguii in three terrestrial environments

Abstract

Mycorrhizal fungi plays important roles in the seed germination and subsequent growth of orchids. The research of fungi in orchid roots, especially dominant mycorrhizal fungi is critical for orchids protection. In this study, the fungal community and composition of mycorrhizal fungi in roots, rhizomes and rhizosphere soil of Bulbophyllum tianguii grown in three terrestrial environments were analyzed by the second generation sequencing technology. The results of OTU clustering and α and β diversity analysis showed that there were significant differences in fungal communities in roots, rhizomes and rhizosphere soil of B. tianguii. The total number of OTUs in rhizomes was much less than that in roots and rhizosphere soil. The number of OTUs in rhizosphere soil and the diversity of mycorrhizal fungi were the highest. Meanwhile, the species and abundance of mycorrhizal fungi in roots and rhizomes of B. tianguii were different from those in rhizosphere soil. For different elevations, compared with B. tianguii that grow in middle of Tiankeng and top of Tiankeng, the OTUs number of B. tianguii in orchid garden is richest, and the diversity of mycorrhizal fungi in orchid garden was significantly higher than other locations. Among the three different habitats of B. tianguii, the number of OTUs in humus soil and stone habitats was notably higher than tree habitats, and the diversity of mycorrhizal fungi in humus soil was the highest. The analysis of mycorrhizal fungi in different habitats and altitudes of B. tianguii showed that Sebacina and Exophiala were the dominant mycorrhizal fungi in B. tianguii. The results of species annotation, phylogenetic tree and co-occurrence network analysis showed the dominant mycorrhizal fungi of B. tianguii mainly included Sebacina, Cladosporium, Exophiala, Fusarium. This study reveals the symbiotic relationship between Sebacina, Exophiala, Cladosporium and the B. Tianguii. It will provide a theoretical basis for the protection and biological function study of B. Tianguii.

Keywords: bulbophyllum tianguii; microbial community; mycorrhizal fungi; orchidaceae; orchids.

Figure 1

Growth situation of B tianguii. [(A): B tianguii; (B): Roots attached to stone walls; (C): Roots attached to humus soil; (D): Roots attached to the trunk.].

Figure 2

Venn chart. Different colors represent different groups, the number of overlapping parts represents the number of species shared by multiple groups, and the number of non-overlapping parts represents the number of species unique to the corresponding group. [(A): root, rhizome and rhizosphere soil groups; (B): different habitat groups; (C): different altitude groups].

Figure 3

Bar diagram of fungal community composition. The ordinate is the sample name, and the abscissa is the proportion of species in the sample. Columns with different colors represent different species, and the length of the column represents the proportion of the species. (A): fungi composition at Phylum level; (B): mycorrhizal fungi composition at Phylum level; (C): fungal composition of the middle of Tiankeng (Phylum); (D): mycorrhizal fungi composition of the middle of Tiankeng (Phylum).

Figure 4

Bar diagram of mycorrhizal fungal community composition. The abscissa is the sample name, and the ordinate is the proportion of species in the sample. Columns with different colors represent different species, and the length of the column represents the proportion of the species. Composition of mycorrhizal fungi is at Phylum (A) and Genus levels (B).

Figure 5

Wilxocon rank sum test of Alpha index difference between groups. The significance of the difference between the two groups is expressed as: 0.01

(A-C): root, rhizome and rhizosphere soil groups; (D–F): different habitat groups; (G–I): different altitude groups.

Figure 6

NMDS analysis. Points of different colors or shapes represent samples of different groups. The closer the two sample points are, the more similar the species composition is. (A): root, rhizome and rhizosphere soil groups; (B): different habitat groups; (C): different altitude groups.

Figure 7

System evolution tree. Each branch represents each OTU, and the branch is colored according to the advanced Phylum level of the species. The length of the branch is the evolutionary distance between the two species, namely the degree of species difference. The column shows the proportion of Reads in different groups.

Figure 8

Co-occurrence network diagram. Co-occurrence relationship of species in different samples is visually displayed. Nodes in the network represent sample nodes or species nodes, and the connection between sample nodes and species nodes represents the sample containing the species. (A): different habitat groups; (B): different altitude groups.